Cosmological abundances of right-handed neutrinos Original Research Article

We study the equilibration of the right-helicity states of light Dirac neutrinos in the early universe by solving the momentum-dependent Boltzmann equations numerically. We show that the main effect is due to electroweak gauge boson poles, which enhance thermalization rates by some three orders of magnitude. The right-helicity states of tau neutrinos will be brought in equilibrium independently of their initial distribution at a temperature above the poles if mντ ⪆ 10 keV.